1 . Field of the Invention
This invention is in the field of compositions and methods for bleaching teeth. More particularly, the invention is in the field of compositions and methods for accelerated bleaching activity using a two-part bleaching system. A first part includes a stable concentrated dental bleaching agent at low pH and a second part includes a base dispersed within a stable gel that, when mixed with the first part, raises the pH of the mixed composition to an acceptable level and, optionally, in order to destabilize the dental bleaching agent and trigger the release of oxygen radicals to accelerate bleaching activity.
2. Review of the Relevant Technology
In the last decade there has been a proliferation of compositions and methods for bleaching teeth. Compositions for both in-office or at-home use typically include a peroxide bleaching agent, such as carbamide peroxide or aqueous hydrogen peroxide. Carbamide peroxide is a complex of urea and molecular hydrogen peroxide. On the other hand, hydrogen peroxide by itself only exists in aqueous form and is generally unstable except at relatively low pH (e.g. 2).
When formulating an appropriate bleaching composition there is inherently a trade-off between stability and reactivity. It is desirable for a bleaching composition to remain stable between the time when it is manufactured and when it is used to bleach a person""s teeth. However, once placed on a person""s teeth it is desirable for the composition to quickly break down and release active oxygen radicals capable of bleaching teeth. One way to obtain long-term stability is to keep the concentration of active bleaching agent relatively low. This, however, has the negative drawback of providing only minimal to modest bleaching activity.
Dental bleaching compositions that include higher concentrations of dental bleaching agent must generally be kept refrigerated to ensure long-term stability and/or kept at relatively low pH (e.g., 2 or less) where refrigeration cannot be guaranteed. In the case where it is desired to mass-produce a highly concentrated dental bleaching composition and then distribute it to many different locations, it is generally impossible to prevent at least a portion of such composition from becoming overheated at some point during shipping and handling. Unless such compositions are maintained at a low pH, their potency can be compromised if they are exposed to excessive heat during shipping. Accordingly, it has heretofore been difficult to manufacture and then distribute bleaching compositions at higher pH that include high concentrations of bleaching agent while avoiding at least partial breakdown of the bleaching agent.
Since highly acidic compositions can etch or otherwise damage teeth if maintained in contact with the teeth for more than a few minutes, it is typically desirable to neutralize an acidic bleaching composition prior to application to a patient""s teeth. In the case where the composition to be applied to the patient""s teeth is intended to have a generally aqueous, non-viscous consistency, neutralization of an acidic aqueous hydrogen peroxide solution by means of a base is straight forward. One simple neutralization method is to add aqueous sodium hydroxide to the aqueous hydrogen peroxide until the pH is raised to the desired level. Depending on the concentration of the hydrogen peroxide and the resulting pH, raising the pH can also have the desired benefit of at least partially destabilizing the hydrogen peroxide so as to accelerate the release of oxygen radicals responsible for bleaching teeth.
Besides sodium hydroxide, there are a variety of bases or buffers that have been used to neutralize the acidity of stable hydrogen peroxide compositions. U.S. Pat. Nos. 5,713,738 and 5,645,428 to Yarborough, for example, discloses the use of sodium carbonate, sodium bicarbonate, calcium carbonate, ammonium hydroxide, potassium hydroxide, or calcium hydroxide to raise the pH of aqueous bleaching compositions so as to accelerate bleaching activity. For purposes of disclosing bases for use in neutralizing acidic hydrogen peroxide compositions, the foregoing patents are incorporated herein by reference.
One of the challenges in manufacturing two-part bleaching systems having an acidic bleaching component and a strong basic component, which are mixed together by the dental practitioner, is the difficulty in obtaining stable gels. Gels are often desirable over runny compositions because they adhere much better to the patient""s teeth compared to non-viscous liquids and stay in place rather than running off the teeth and onto surrounding soft oral tissues. Gels having a certain level of stickiness and viscosity are also desirable when using custom-fitting dental trays known in the art and exemplified by those disclosed in U.S. Pat. No. 5,376,006. For purposes of disclosing custom dental trays for bleaching teeth, the foregoing patent is incorporated herein by reference.
The ability to obtain a stable gel is particularly difficult where it is desired to use a polymeric tackifying agent such as carboxypolymethylene. Carboxypolymethylene is unable to maintain its desired stickiness and gelling capabilities over time when mixed with either concentrated acidic aqueous hydrogen peroxide solutions or strongly basic solutions used to neutralize the acidic hydrogen peroxide solution. Where it is desired to mass produce highly concentrated yet stable hydrogen peroxide bleaching compositions, it has heretofore been necessary to entirely replace carboxypolymethylene and like polymers with non-polymeric thickeners such as fumed silica in order to obtain stable gels.
In view of the foregoing, it would an advancement in the art to provide improved two-part dental bleaching systems and methods of manufacturing such systems in order to yield a mixed composition that is a stable gel containing a polymeric thickening agent. It would be a further advancement if such two-part systems could be manufactured so as to yield at least one component that could exist over time as a stable gel that includes a polymeric thickening agent. It would yet be an advancement to provide a concentrated low pH aqueous hydrogen peroxide bleaching composition in one part and a stable gel that included a polymeric thickening agent and strong base in another part for mixing with and at least partially neutralizing the acidic bleaching composition.
Such compositions and methods for providing multi-part dental bleaching systems that include at least one component that is a stable gel are disclosed and claimed herein.
The present invention relates to dental bleaching compositions and methods for manufacturing and using such compositions to bleach teeth. More particularly, the invention encompasses multi-part dental bleaching systems that comprise a first part (or composition) that includes a concentrated and stable dental bleaching agent and a second part (or composition) that includes a strong base dispersed within a stable gel that has good long-term stability.
The two-part systems are stable with respect to both bleaching potency and the maintenance of a gel have a desired range of stickiness and/or viscosity gel during transport and subsequent storage. Upon mixing the two parts together a bleaching gel composition having a desired bleaching potency can be formed. This allows the two-part composition to be manufactured and then shipped and stored as desired prior to mixing the parts together without any significant loss in bleaching potency and the breakdown of the gel that includes the strong base. The invention also encompasses methods of manufacturing the inventive multi-part dental bleaching systems, as well as methods for bleaching a person""s teeth using such systems.
A first part or composition of the inventive dental bleaching system includes a dental bleaching agent. There are a variety of dental bleaching agents capable of releasing oxygen radicals. The most commonly used dental bleaching agents are based on hydrogen peroxide, including aqueous hydrogen peroxide or complexes of hydrogen peroxide, such as urea peroxide or a perborate (e.g., sodium perborate monohydrate). Sodium perborate monohydrate is a complex of sodium borate and molecular hydrogen peroxide. In one embodiment, the dental bleaching agent will advantageously comprise a concentrated aqueous solution of hydrogen peroxide (e.g., about 20-90% hydrogen peroxide, preferably about 30-60% hydrogen peroxide).
The pH of the first part or composition (i.e., the part that includes the dental bleaching agent) will typically be on the acidic side of the pH scale, generally less than about 5. In order to maintain the stability of the first part or component, particularly in the case where constant refrigeration cannot be ensured, it may be desirable to adjust the pH to below about 4, preferably to a pH between about 1-2. The naturally low pH of aqueous hydrogen peroxide solutions can further be lowered by adding one or more acids in order to further increase stability (e.g., citric acid, which can also act as an ion scavenger).
The first part or composition may include optional additives in addition to the dental bleaching agent such as ion scavengers (e.g. EDTA or citric acid) or other stabilizing agents, other thickening agents (e.g., fumed silica or gums), liquid polyols (e.g., PEG), and light-energy absorbing agents (e.g. carotene). Highly concentrated hydrogen peroxide bleaching compositions containing a variety of optional additives and adjuvents are set forth in U.S. Pat. No. 5,858,332 to Jensen et al. For purposes of disclosing highly concentrated dental bleaching compositions, as well as adjuvents and additives that may be included within such compositions, the foregoing patent is incorporated herein by reference.
A second part or composition of the inventive bleaching systems according to the invention includes a strong base in particulate form dispersed within a stable gel that includes a polymeric thickening agent. Examples of suitable bases include oxides, hydroxides, and carbonates of alkali and alkaline earth metals (e.g., finely ground potassium hydroxide). Examples of suitable polymeric thickening agents include carboxypolymethylene (which broadly includes carboxypolymethylene at any pH and at any degree of neutralization) PEMULEN, a proprietary composition available from B.F. Goodrich, and compositional or chemical equivalents thereof The second part may also include additional components such as ion scavengers, other thickening agents, liquid polyols, and light-energy absorbing agents.
In order to maintain the stability of the polymeric thickening agent, it is typically advantageous for the second part or composition to be substantially water free, preferably essentially anhydrous, since water is believed to hydrolyze or otherwise affect the stability of the polymeric thickening agent when mixed with a strong base. Because the second part is essentially water free, it does not technically have a pH. However, due to the inclusion of a strong base, the pH of the second part would typically be about 12-14 if mixed with sufficient water to produce a reliable pH reading.
Upon mixing the first and second parts together, typically by the dental practitioner who will administer the bleaching composition to a patient""s teeth, the base-containing component raises the pH of the bleaching agent so as to yield a mixed composition having a pH between about 4 and 11, more preferably between about 5 and 9, and most preferably between about 6 and 8. After mixing the two parts together, the mixed composition may either be used immediately by the dental practitioner for bleaching or else stored in a refrigerator for later use. Depending on the concentration of the dental bleaching agent, and/or the pH of the resulting mixed composition, and/or whether the mixed composition includes other components that affect the stability (e.g., stabilizing or destabilizing agents), the dental practitioner can optimize or adjust the stability of the mixed dental bleaching composition to suit the particular needs of the dental practitioner.
The relative stability or instability of the mixed dental bleaching composition depends, at least in part, on the pH, the temperature, and the relative concentration of the bleaching agent in the mixed composition. In general, the higher the pH and warmer the temperature, the less stable will be the bleaching agent at a given concentration. Accordingly, where it is desired to accelerate bleaching activity, the dental practitioner may wish to further raise the pH of the mixed composition in order to trigger the release of oxygen radicals, which are believed to be responsible for bleaching teeth. On the other hand, where it is desired to form a batch of mixed bleaching composition that can be stored in refrigeration for later use, it may be desirable to keep the pH at a level that does not trigger the release of oxygen radicals for a given concentration of bleaching agent.
The mixed composition will typically be used by dental practitioners during in-office procedures. This is particularly true for mixed compositions having relatively high concentrations of dental bleaching agent (e.g., about 20-90% available hydrogen peroxide), which are typically not suitable for at-home use. Nevertheless, the compositions of the present invention are not limited to any particular use or application and broadly include any two- or multi-part dental bleaching system that includes a bleaching agent in one part and a strong base dispersed within a stable gel in another part. Thus, home use products that incorporate the inventive multi-part bleaching systems disclosed herein are certainly within the scope of the invention.
These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.
The present invention relates to dental bleaching compositions and methods for manufacturing and using such compositions to bleach teeth. More particularly, the invention encompasses multi-part dental bleaching systems that comprise a first part (or composition) that includes a concentrated and stable dental bleaching agent and a second part (or composition) that includes a strong base dispersed within a gel based on a polymeric thickening agent that has good long-term gel stability.
The two-part systems are stable over time with respect to bleaching potency, stickiness, viscosity, and gelation during transport and subsequent storage. Keeping the first part containing the bleaching agent at a lower pH helps maintain bleaching potency during transport and storage. Similarly, maintaining the second part substantially free of water helps to maintain the desired gel properties during transport and storage. Consequently, upon mixing the two parts together, a stable bleaching gel having a desired bleaching potency can be formed. This allows the two-part composition to be manufactured and then shipped and stored as desired prior to mixing the parts together without any significant loss in bleaching potency and the breakdown of the gelation properties of the polymeric thickening agent by the strong base.
The invention also encompasses methods of manufacturing the inventive multi-part dental bleaching systems, as well as methods for bleaching a person""s teeth using such systems.
The dental bleaching systems according to the present invention include at least two different parts or compositions that are manufactured and advantageously stored and transported separately so as to maximize the desired properties of the final mixed composition, as noted above. At a minimum, a first part or component will include a dental bleaching agent, preferably in concentrated form, and at preferably low pH. A second part or composition will include a base dispersed within a stable gel. The two parts or compositions may include other additives or adjuents as desired to yield mixed compositions that have desired properties. It is also within the scope of the invention to include additional parts or compositions that can be mixed with parts one and two which are discussed more fully below.
A. Part One
A first part or composition of the inventive dental bleaching system includes a dental bleaching agent. There are a variety of dental bleaching agents capable of releasing oxygen radicals. The most commonly used dental bleaching agents are based on hydrogen peroxide. Examples include aqueous hydrogen peroxide and complexes of hydrogen peroxide, such as urea peroxide, perborates (e.g., sodium perborate monohydrate), and peroxyacetic acid. Sodium perborate monohydrate is a complex of sodium borate and molecular hydrogen peroxide.
The dental bleaching agent may be included in any amount so as to yield a mixed composition having a desired concentration and potency. In general, the multi-component systems of the present invention are particularly useful in maintaining the bleaching strength of bleaching agents that are contained in higher concentrations. In general, the concentration of available hydrogen peroxide may range from as low as 3% to as high as 95% by weight of the bleaching composition (i.e., part one), preferably in a range from about 20% to about 90% by weight, more preferably in a range from about 30% to about 70% by weight, most preferably in a range from about 40% to about 60% by weight of the bleaching composition. In a presently preferred embodiment, the bleaching agent includes aqueous hydrogen peroxide. Nevertheless, it is certainly within the scope of the invention to augment or substitute some or all of the aqueous hydrogen peroxide with any other known bleaching agent.
The dental bleaching agent may advantageously be mixed with other components as desired to yield a bleaching component having the desired properties. For example, it may be desirable to include one or more polyols such as glycerin, sorbitol, propylene glycol, polypropylene glycol, and polyethylene glycol within part one. Thickeners that are stable in the presence of strong bleaching agents may also be included, an example of which is fumed silica. Ion scavengers (e.g. EDTA and citric acid) or other stabilizing agents, other thickening agents (e.g., gums), flavorants, and light-energy absorbing agents (e.g. carotene) may be included as desired.
The pH of the bleaching part or composition will typically be on the acidic side of the pH scale, generally less than about 5. In order to maintain the stability of the first part or component, particularly in the case where constant refrigeration cannot be ensured, it may be desirable to adjust the pH to below about 4, preferably to a pH between about 1-2. Aqueous hydrogen peroxide naturally results in a low pH solution, although commercial grades of hydrogen peroxide may include a strong acid to further lower the pH to a desired level. Citric acid can stabilize the peroxide by both lowering the pH and acting as an ion scavenger.
The bleaching part or component is preferably substantially free of abrasives, since abrasives (otherwise known as polishing agents) common to toothpastes may trigger or catalyze the destabilization of the dental bleaching agent. Nevertheless, it is certainly within the scope of the invention to include an abrasive.
B. Part Two
A second part or composition of the inventive bleaching systems according to the invention includes a strong base mixed within a stable gel that includes a polymeric thickening agent. The base is advantageously in a nonsolubilized and particulate form to prevent or reduce any negative reactions between the base and thickening agent. The base may include any appropriate base in a form so that it does not destroy or inhibit the long-term gelling properties of the second part or composition. However, the finer the particulate the more dispersed will be the base within the gel. The base may be obtained in powder form, or it may be obtained as pellets or flakes and subsequently ground using any appropriate grinding means and methods known in the art (e.g., wet grinding using an appropriate liquid and a grinding mill).
Examples of suitable bases include oxides, hydroxides, and carbonates of alkali and alkaline earth metals, which are crystalline solids and which can be ground into fine powders and dispersed in particulate form within a gel that is substantially free of water. The concentration or amount of added base may be selected so as to yield a final mix composition having a desired pH. Because the pH of the final composition depends on a variety of factors, such as the pH of the bleaching part or component, the desired pH of the mixed composition, the relative quantities of parts one and two, and the concentration, if any, of any additional components added to the final mixture, as well as the relative strength of the base, there is no preferred concentration range for the base within part two.
A wide variety of thickening agents may be used within the scope of the invention, including both polymeric thickening agents and finely divided particulates. The second part or composition will, at a minimum, include at least one polymeric thickening agent. Examples of suitable polymeric thickening agents include carboxypolymethylene, PEMULEN, PLURONIC, cellulosic ethers, polysaccharide gums, proteins, starches, and the like. The second part may also include additional components such as ion scavengers (e.g., EDTA), particulate thickening agents (e.g., fumed silica), liquid polyols, and light-energy absorbing agents (e.g., carotene).
Carboxypolymethylene is a well-known thickening agent utilized in dental bleaching compositions and a wide variety of other compositions. It is a slightly acidic vinyl polymer with active carboxyl groups. Suitable carboxypolymethylene compositions may be obtained from B.F. Goodrich Co. under the trade name CARBOPOL. For purposes of this disclosure and the appended claims, the term xe2x80x9ccarboxypolymethylenexe2x80x9d shall broadly include carboxypolymethylene at any pH and any degree of neutralization with a base.
One currently preferred carboxypolymethylene resin is known by the trade name CARBOPOL 934P CARBOPOL 934P is a high purity pharmaceutical grade of CARBOPOL 934, having an approximate molecular weight of about 3 million. Another preferred carboxypolymethylene is CARBOPOL 974P NF, which has more recently surpassed CARBOPOL 934P as the carboxypolymethylene of choice in many compositions.
PEMULEN is a trade name of B.F. Goodrich and is used to identify high molecular weight, cross-linked copolymers of acrylic acid and a hydrophobic comonomer. The exact composition of PEMULEN is unknown since it is a proprietary formulation of B.F. Goodrich.
The name PLURONIC describes a range of polymers available from BASF, which are also known as poloxamers. The term xe2x80x9cpoloxamerxe2x80x9d is the CFTA name for polyoxyethylene polyoxypropylene block copolymers. An example includes POLOXOMER 407, also known as PLURONIC F127.
In order to form a stable gel, the second part or component will also typically include an appropriate solvent for the gelling agent, such as a liquid polyol. Examples of suitable polyols include, but are not limited to, glycerin, propylene glycol, polypropylene glycol, polyethylene glycol, sorbitol, and the like.
In order to maintain the stability of the polymeric thickening agent, it is typically advantageous for the second part or composition to be substantially water free, preferably essentially anhydrous, since water is believed to hydrolyze or otherwise affect the stability of the polymeric thickening agent when mixed with a strong base. Because the second part is essentially water free, it does not technically have a pH. However, due to the inclusion of a strong base, the pH of the second part would typically be about 12-14 if mixed with sufficient water to produce a reliable pH reading. It is also preferable for the second part to be substantially free of abrasives, although it would certainly be within the scope of the invention to include an abrasion.
C. Mixed Composition
In general, the relative concentrations of part one and part two will range from about 1:2 to about 5:1. Nevertheless, it is within the scope of the invention to utilize parts one and two in any desired ratios that yield a desired mixed composition. In general, it will be advantageous for part one to predominate in order to obtain a final mixed composition having a relatively high concentration of bleaching agent. In general, a smaller quantity of a strong base can be used to neutralize a greater quantity of the acidic bleaching composition, such that it may be feasible for the ratio of part one to part two to be as high as about 10:1 or more.
Upon mixing the first and second parts together, typically by the dental practitioner who will administer the bleaching composition to a patient""s teeth, the base-containing component raises the pH of the bleaching agent so as to yield a mixed composition having a pH between about 4 and 11, more preferably between about 5 and 9, and most preferably between about 6 and 8. After mixing the two parts together, the mixed composition may either be used immediately by the dental practitioner for bleaching or else stored in a refrigerator for later use. Depending on the concentration of the dental bleaching agent, and/or the pH of the resulting mixed composition, and/or whether the mixed composition includes other components that affect the stability (e.g., stabilizing or destabilizing agents), the dental practitioner can optimize or adjust the stability of the mixed dental bleaching composition to suit the particular needs of the dental practitioner. The relative stability or instability of the mixed dental bleaching composition depends, at least in part, on the pH, the temperature, and the relative concentration of the bleaching agent in the mixed composition. In general, the higher the pH and warmer the temperature, the less stable will be the bleaching agent at a given concentration. Accordingly, where it is desired to accelerate bleaching activity, the dental practitioner may wish to further raise the pH of the mixed composition in order to trigger the release of oxygen radicals, which are believed to be responsible for bleaching teeth. On the other hand, where it is desired to form a batch of mixed bleaching composition that can be stored for later use, it may be desirable to keep the pH at a level that does not trigger the release of oxygen radicals for a given concentration of bleaching agent and at the expected storage temperature. The mixed compositions of the invention will preferably be substantially or entirely free of abrasives, although the use of an abrasive is not foreclosed.
The mixed compositions will typically be used by dental practitioners during in-office procedures. This is particularly true for mixed compositions having relatively high concentrations of dental bleaching agent (e.g., about 20-90% available hydrogen peroxide), which are typically not suitable for at-home use. Nevertheless, the compositions of the present invention are not limited to any particular use or application and broadly include any use that involves two- or multi-part dental bleaching systems that include a bleaching agent in one part and a strong base dispersed within a stable gel in another part. Thus, home-use products that incorporate the inventive multi-part bleaching systems disclosed herein are certainly within the scope of the invention.
Whereas raising the pH of the mixed composition generally accelerates the bleaching activity of the dental bleaching agent, it may be further desirable for the dental practitioner to further accelerate the bleaching activity by applying light or heat energy (e.g. by means of a dental curing light, a heat lamp, a dental light guide, or a laser). The inclusion of carotene or other light energy absorbing agents within the mixed composition facilitates the acceleration of bleaching activity through the application of radiant energy.
In the case where the mixed composition is used in an at-home bleaching regimen, it will be preferable to apply the composition using a soft, flexible, custom-fitting dental tray known in the art. Nevertheless, it should be understood that any dental tray known in the art, even thick athletic mouth guards and the like, may be used to apply the dental bleaching compositions according to the present invention.